The present invention relates generally to antenna feed architectures, and more particularly, to an antenna feed architecture employing a folded multistage, multilevel network of dissimilar constant reflection-coefficient components, which serves to efficiently match dissimilar radiator (load) and line-source (source) impedance over a wide range of operating frequencies and scan angles.
The performance of E-plane bends, E-plane T-junctions and E-plane step transformers in conventional rectangular waveguide operating in a dominant TE.sub.1,0 mode is described extensively in the literature. For example, see Montgomery, C. G., R. H. Dicke and E. M. Purcell (eds.), "Principles of Microwave Circuits" (MIT Radiation Lab. Ser. No. 8), pp. 188-191, 285, McGraw-Hill, New York, 1951, Marcuvitz, N. (ed.), "Waveguide Handbook" (MIT Radiation Lab. Ser. No. 10), pp. 307-310, 333-334, 336-350, McGraw-Hill, New York, 1951, Moreno, T., "Microwave Transmission Design Data", pp. 157-164, Artech House, Norwood, Mass., 1989, and Matthaei, G. L., L. Young and E. M. T. Jones, "Microwave Filters, Impedance Matching Networks, and Coupling Structures", pp. 258-259, 522-531 and 576-581, Artech House, Norwood, Mass., 1980. These elements are generally restricted to operating frequency bandwidths much less than 40 percent due to the inherent dispersive properties of rectangular waveguide structures. It is therefore conventional to utilize individually matched (minimized reflection coefficient) narrowband implementations of these devices an any integrated structure (such as a feed network) employing a plurality of these components.
Qualitatively, similar performance is obtained for such E-plane circuits that operate in the TEM mode in parallel-plate waveguide, or if the sides are bounded by conducting walls, in TE.sub.m,0 modes. However, quantitatively, in contrast to rectangular waveguide implementations, parallel-plate implementations of E-plane bends, tees, and steps can exhibit multi-octave frequency ranges for which their individual impedance properties are essentially constant, due to the nondispersive nature of the parallel-plate structure. In addition, and again in contrast to rectangular waveguide implementations, H-plane scanning of the plane-wave radiating from the antenna structure can be easily realized in the single continuous transverse structure of the parallel-plate as compared to the difficulty in realizing H-plane scanning in a rectangular waveguide structure having numerous discrete, mutually-coupled, complex waveguide feeds. Likewise, the scanangle dependence of each stage is readily derived and therefore readily utilized in optimization of performance over scan angle.
Accordingly, it is an objective of the present invention to provide for an improved antenna feed architecture employing a folded multistage, multilevel network of constant reflection-coefficient components in order to realize a simple integrated feed structure capable of high efficiencies over a wide range of operating frequencies and scan ranges.